Coatings that provide low reflectivity or a high percent transmission over a broad wavelength range of light are desirable in many applications including semiconductor device manufacturing, solar cell manufacturing, and glass manufacturing. The refractive index of a material is a measure of the speed of light in the material which is generally expressed as a ratio of the speed of light in vacuum relative to that in the material. Low reflectivity coatings generally have a refractive index (n) between air (n=1) and glass (n˜1.5).
An antireflective (AR) coating is a type of low reflectivity coating applied to the surface of a transparent article to reduce reflectivity of visible light from the article and enhance the transmission of such light into or through the article thus decreasing the refractive index. One method for decreasing the refractive index and enhancing the transmission of light through an AR coating is to increase the porosity of the antireflective coating. Porosity is a measure of the void spaces in a material. Although such antireflective coatings have been generally effective in providing reduced reflectivity over the visible spectrum, the coatings have suffered from deficiencies when used in certain applications. For example, porous AR coatings which are used in solar applications are highly susceptible to moisture absorption. Moisture absorption can lead to an increase in the refractive index of the AR coating and corresponding reduction in light transmission.
Thus, there is a need for AR coatings which exhibit increased transmission, reliability and durability.